1. Field of the Invention
The invention relates to a method of manufacturing a fuel cell. More particularly, the invention relates to a method of manufacturing a fuel cell in which an electrode layer is formed of Carbon NanoTubes (CNTs).
2. Description of Related Art
Japanese Patent Application Publication No. 2007-257886 (JP-A 2007-257886) discloses a method of manufacturing a fuel cell. This method includes the step of (1) growing carbon nanotubes (CNTs) perpendicular to a substrate composed of a catalyst for growing CNTs supported on a base plate and the base plate, (2) hot-pressing the CNTs to a polymer electrolyte membrane, and (3) peeling the substrate from the CNTs. In this method, hot-pressing is carried out with the CNTs and the polymer electrolyte membrane heated to from 140° C. to 160° C. and pressurized to from 2 to 3 MPa.
The CNTs are peeled from the substrate by tearing off the substrate in a direction away from the polymer electrolyte membrane. Hence, when the substrate is peeled off, there is a possibility of the CNTs separating from the polymer electrolyte membrane together with the base material. In light of this, according to JP-A 2007-257886, because pressure is applied at the time of hot-pressing, it is possible to cause the CNTs to become embedded in the polymer electrolyte membrane. Consequently, when the base material is peeled off, the CNTs can be prevented from separating from the polymer electrolyte membrane together with the base material.
However, when pressure is applied to the CNT layer at the time of hot-pressing, the CNTs that was formed in the perpendicular direction sometimes deforms. Also, depending on the degree of pressure applied at the time of hot-pressing, the CNTs sometimes penetrate too deeply into the polymer electrolyte membrane. In cases where the CNTs have penetrated too deeply and passed through the polymer electrolyte membrane, there is a possibility that a leak will arise where the reactant gas passes from one electrode to the other electrode side. This has led at times to a decline in fuel cell performance.